[petsc-users] Two PCs on same residual in multiplicative fashion !

[Abdul Hanan Sheikh]

Thank you Matt, your assumption is alright. It was typo. 

I got this idea , yet if I want to invert P2 exactly by PCLU then how should I do ?? 


This is indeed, but I avoid to merge(matrix product) for some reasons. 


Thanks again. 

Abdul




>________________________________
> From: Matthew Knepley <knepley at gmail.com>
>To: Abdul Hanan Sheikh <hanangul12 at yahoo.co.uk>; PETSc users list <petsc-users at mcs.anl.gov> 
>Sent: Friday, 26 October 2012, 18:22
>Subject: Re: [petsc-users] Two PCs on same residual in multiplicative fashion !
> 
>
>On Fri, Oct 26, 2012 at 12:04 PM, Abdul Hanan Sheikh <hanangul12 at yahoo.co.uk> wrote:
>
>
>>
>>Dear Developers and members, 
>>
>>
>>
>>I intend to solve system Ax=b with two preconditioners as follows: 
>>
>>
>>
>>P1^{-1} P2^{-1} A x = P^{-1} P^{-1} b
>
>
>I assume you mean P1^{-1} P2^{-1} A x = P1^{-1} P2^{-1} b
>
>
>
>
>With this setup, I think its easiest to use PCKSP with the matrix for
>the KSP being P2. That would give you
>
>
>  P2^{-1} A x = P2^{-1} b
>
>
>Now you can precondition that solve with another PCKSP with the matrix
>for that KSP being P1, and get what you want.
>
>
>This seems like a strange thing since you could just merge those matrices.
>
>
>   Matt
> 
>where P1 and P2 are exclusively available as matrices. 
>>
>>This might be crazy to many. 
>>
>>
>>
>>I thought to start with PCCOMPOSITE but i do not think it does exactly what I intend. 
>>
>>
>>Any Idea would be appreciated. 
>>
>>
>>
>>A beginner!!! 
>>Abdul
>>
>
>
>
>-- 
>What most experimenters take for granted before they begin their experiments is infinitely more interesting than any results to which their experiments lead.
>-- Norbert Wiener
>
>
> 
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